Colors by Carl Reynolds “Color is an immensely complex subject, one that draws on concepts and results from physics, physiology, psychology, art, and graphic design. The color of an object depends not only on the object itself, but also on the light source illuminating it, on the color of the surrounding area, and on the human vision system.” ! Computer Graphics Principles and Practice ! — Foley & van Dam1 We were all taught in school that the primary colors are red, yellow, and blue. This statement implies, all colors can be created from mixing various amounts of red, yellow, and/or blue. This is wrong. Red, yellow, and blue are not the primary colors. Neither are red, green, and blue; or cyan, magenta, and yellow. Each of these is a set of primary colors, but no finite set of colors can be used to create all the colors visible to the human eye. It might be better to call these a color space, instead of primary colors. It is possible to create all the colors within the red-yellow-blue space, by using various amounts of red, yellow, and/or blue, but there are colors outside this space that are visible to the human eye. Figure 1. Depending on what you’re doing, you might want to use one, or another color space. For example, most painters use red, yellow, and blue, along with black, and white. If you’re printing color magazines, or books you’ll probably use cyan, magenta, yellow, and black to do your designs. Many computer graphics artists design their work using red, green, and blue. If you’re creating textiles, you will probably use red, yellow, and 1 J. Foley, A. van Dam, S. Feiner, J. Hughes. Computer Graphics Principles and Practice, pages 563-585. Addison-Wesley, second edition, 1990. Colors!Carl Reynolds © 2014!Page 1 blue. The space you use will depend largely on what you’re accustomed to and which one work best with the medium of your choice. Almost any three colors can serve as primary colors, depending on how you want to use them. The only relevant issues are (1) the actual range of mixtures (gamut) you are able make with the colorants, and (2) whether this gamut produces the desired visual effect in the images you want to represent. ! — Bruce MacEvoy 2 What do we mean by all colors? We must recognize that there are colors outside the range of the human eye. A spectrum of “all colors” might look something like Figure 1. Note that there are no non-spectral colors, such as magenta, and that colors in the infrared and ultraviolet ranges, not visible to most humans, are bands of black. The range of wavelengths3 for Figure 1 extends far outside the normal human range. Depending on the species, butterflies have five or six types of color receptors4. Mantis shrimp, with 16 types of receptors, can see deep into the ultraviolet. Sparrows with four types of color receptors see into the extreme infrared, and perceive many more greens and blues than humans. When younger I could see several different bands of color on both sides of the spectrum into the ultraviolet and infrared. As I’ve aged, I can no longer see these extra colors, leading me to believe that all of us can see different ranges of color, making each of us unique in our abilities to see various colors, not only from each other, but even from ourselves at different times of our lives. In the 1850s while doing color matching experiments James Clerk Maxwell noticed large individual differences in color perception among his test subjects, leading to physiological complexities in the measurement of color vision. These arise from the prereceptoral filtering of blue and violet light by the lens and macular pigment, and from individual differences in cone sensitivity and photopigments, and in the proportional numbers of long, medium and short cones5 in the retina. 2 http://www.handprint.com/HP/WCL/color6.html 3 My preference is to refer to the frequency of various colors. My second choice would be to measure the wavelength of light in angstroms (10-10 meters), but most color scientists measure light by its wavelength in nanometers so I will use the standard abbreviation ‘nm’ when referring to light measurements in this article. 4 Humans normally have three types of color receptors. I use ‘normally’ in the mathematical sense. There are some people who have limited or no use of some of the three receptor types (we refer to these people as “colorblind”). There may be people who have the use of four color receptors. However, on a Gaussian distribution, normal is to have adequate use of three color receptors. 5 The terms ‘long’, ‘medium’, and ‘short’ refer to the wavelengths of the light that the three visual receptors in the human eye are most sensitive to. ‘Long’ receptors are sensitive to wave lengths from about 480 nanometers to about 740nm. Their peak sensitivity is around 575nm. The medium receptors have a peak sensitivity around 545nm, and the short receptors peak sensitivity is around 435nm. Colors!Carl Reynolds © 2014!Page 2 Ancient Color Usage History shows that humans have always been attracted to color. We have found paintings in red, orange, dark purple, brown, orange, and dark green using powdered earths and plants on cave walls up to 40,000 years old.6,7 The Ancient Egyptians from as early as 2650b.c.8 and the ancient Greeks from c. 530b.c. created paintings on vases, walls, and panels using powdered earth, and glass to make glazes and stucco. The Greeks used white, black, red, orange, and some green9. Ancient Egyptians are the only culture before the Renaissance Figure 2. known to use blue. Their colors included white, black, red, orange, yellow, green, and purple10. The Romans used dry painting techniques, and frescos to create a large variety of paintings11. Tempera paints are made by adding pigments to prepared egg yolks. The egg dries very quickly and the consistency of the color achieved can vary from batch to batch so it must be used quickly12,13. You don’t want to mix too much at a time because of spoilage, but you want to mix enough to cover the desired area because of difficulty mixing a second batch to match the first. Tempera and water color paints had been used from the time of the Ancient Egyptians, possibly even earlier14. While tempera was widely used until the Renaissance, water colors were only used for sketches, and manuscript illustrations until Albrecht Dürer (1471–1528), started using it to create a number fine wildlife, and landscape paintings in the German Renaissance15. Although the use of oil paints may have been discovered much earlier in other cultures, most Renaissance sources credit the Flemish artist Jan van Eyck (c.1390-c.1441) with 6 http://en.wikipedia.org/wiki/Cave_painting 7 http://wiki.answers.com/Q/What_did_aboriginal_people_use_to_paint_with 8 http://www.crystalinks.com/egyptart.html 9 http://www.essential-humanities.net/western-art/painting/greek 10 http://www.crystalinks.com/egyptart.html 11 http://en.wikipedia.org/wiki/Roman_art 12 http://www.renaissanceconnection.org/lesson_science_egg.html 13 http://www.renaissanceconnection.org/lesson_art_oil.html 14 http://en.wikipedia.org/wiki/Tempera 15 http://en.wikipedia.org/wiki/Watercolor_painting Colors!Carl Reynolds © 2014!Page 3 the invention of oil paints16. In the 1470s an oil painting by Hugo van der Goes arrived in Florence17 and is thought to have influenced Leonardo da Vinci (1452-1519) to become the first painter in Florence to use oil paints. We believe the Ancient Greeks arranged colors in the following order: black, red, green, yellow, white (from dark to light). From his notes, we know that one of the ways Leonardo da Vinci arranged color was white, yellow, brown, red, green, and blue18 (from light to dark). This scheme allowed him to improve on the technique of drawing and painting called chiaroscuro, and expand its use in the art world. Da Vinci also worked with palettes such as red, Figure 3. yellow, blue, green, black, and white, calling these the simple colors, but, he acknowledged that greens and blues were actually complex colors because they could be created by combining other colors19. It is possible that we see Leonardo da Vinci on the cusp of a time when people were shifting from the use of one organization of colors (arranged from dark to light) to another (arranged in color mixing order). Chalks, and glazes are not conducive to being mixed; when you try, you get a mixture of particles, but the colors themselves don’t mix. Because water colors and tempera paints dry so quickly, attempts to mix their colors usually result in a muddy-grey mess. Because of the nature of these media, it’s unlikely that much work was done with color mixing before the introduction of oil paints. It is probable that the introduction of oil paints allowed people, for the first time, to successfully mix paints and see the creation of a different color. Oil may have been the spark that started the interest in answering questions such as “What colors can be used to make another color?”; and “Is there a minimal set of colors that can be used to make all the other colors?”. Keep in mind that the range of colors from which to select a set of primary colors was limited by the colors of oil paints available. Today, we might pick cyan, magenta, and yellow as primary colors (as printers using inks did in the eighteenth century), but, in the 1500s cyan was thought of as a combination of blue and white, and magenta didn’t exist until 185920.